title: Diradical character dependences of the first and second hyperpolarizabilities of asymmetric open-shell singlet systems.
abstract: The static first and second hyperpolarizabilities (referred to as β and γ, respectively) of asymmetric open-shell singlet systems have been investigated using the asymmetric two-site diradical model within the valence configuration interaction level of theory in order to reveal the effect of the asymmetric electron distribution on the diradical character and subsequently on β and γ. It is found that the increase of the asymmetric electron distribution causes remarkable changes in the amplitude and the sign of β and γ, and that their variations are intensified with the increase of the diradical character. These results demonstrate that the asymmetric open-shell singlet systems with intermediate diradical characters can exhibit further enhancements of β and γ as compared to conventional asymmetric closed-shell systems and also to symmetric open-shell singlet systems with intermediate diradical characters.
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan. mnaka@cheng.es.osakau.ac.jp
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Nakano
authors.forename: Benoît
authors.initials: B
authors.lastname: Champagne